The present invention relates to an anode circuit for the final stage of a short-wave transmitter in a coaxial line system wherein a first conductor and a wall of the housing are arranged coxially to the transmitting tube.
In short-wave transmitters for the frequency range between 3 and 30 MHz, the output amplifier incorporates a power tube which has an anode circuit of special configuration. The anode circuit, from which the energy is coupled by way of an inductive matching unit, is provided with tuning elements. In general, the anode circuit consists of a discrete variable inductance and a discrete variable capacitance. A further variable inductance connected in series is provided for matching the tube to the load and to couple the energy from the anode circuit. A variable anode inductance in the form of a coil has the disadvantage that it gives rise to spurious resonances originating from its active and its passive parts. If such resonances coincide with harmonics of the transmitting frequency, they can lead to flashovers, cause damage to high-frequency contacts or lower the efficiency of the transmitter. In VHF technology, therefore, a known procedure consists of shifting this spurious resonance to much higher frequency ranges and greatly reducing the coupling between active and passive parts of the inductance by using coaxially arranged anode circuits in which the load is coupled directly to the inner conductor. Transferring this concept to short-wave transmitters, however, would result in the anode circuit being unacceptably tall. Accordingly, this technique though established for VHF, has hitherto not been applied to short-wave transmitters.